1. Field of the Invention
The present invention relates to a method for incorporating metal oxide synergists into fire retardant compositions. More particularly, it relates to a method for preparing fire retardant styrenic molding compositions which contain halogen fire retardant additives and a metal oxide such as antimony oxide.
2. Description of the Prior Art
Increasing emphasis is being placed on the fire retardant properties of polymers which are used in vehicles, the building trades and consumer goods, e.g., furniture, radio and television cabinets, appliance housings, etc. Most of the polymers that are currently used in the above applications have a tendency to burn. Consequently, steps must be taken to improve fire retardant properties of these polymers in order to make them slower to ignite and slower to burn.
One approach to obtaining fire retardancy is to compound the polymer with fire retardant additives. Halogenated additives, which are used in combination with a synergist such as antimony oxide, are widely used to obtain some degree of fire retardancy.
However, there are problems associated with the additive approach. One such problem is obtaining a uniform blend of polymer and additives. Lack of homogeneity in the blend may give rise to poorer fire retardant ratings as determined by the UL-94 test. Another problem is minimizing the loss of impact strength that occurs when the polymer is formulated with the fire retardant additives.
A need exists in the art for an improved method for compounding polymers with fire retardant additives in order to provide fire retardant compositions with a high degree of homogeneity while minimizing any loss in physical properties such as impact strength.